This invention claims priority to German patent application no. 198 19 447.1 filed on Apr. 30, 1998, and PCT application Ser. No. PCT/EP99/02859 filed on Apr. 28, 1999.
1. Field of the Invention
The present invention is in the field of mixing and washing liquids and/or solids. In particular the present invention concerns non-invasive mixing and washing processes which involve relatively highly viscous liquids.
The present invention concerns a device for mixing liquids and/or solids comprising
a holder for a mixing vessel which is rotatably mounted such that a mixing vessel located in the holder can be rotated about its longitudinal axis,
a drive which can rotate the holder alternately in a clockwise and anti-clockwise direction,
a programmable control unit which regulates the angular excursion of the holder in a clockwise and anti-clockwise direction and in which the angular excursion is stored.
2. Description of Related Art
Many mixing methods are known in the prior art such as invasive mixing methods in which a stirrer or such like is immersed in a vessel containing the substances to be mixed. Such invasive mixing methods are disadvantageous especially in the analytical field since the stirrer can cause contamination and carry-over. Hence in the analytical field non-invasive mixing methods such as vortex mixing are preferred. In this type of mixing, a vessel with its contents is set in motion. The motion can for example be a simple backwards and forwards oscillation but usually the vessel movements are in the shape of an eight or other Lissajou""s figures. However, a disadvantage of vortex mixing is the relatively strong vibrations that it causes and the risk of aerosol formation.
Other mixing methods are known in the prior art in which a vessel is rotated about its longitudinal axis in order to mix the liquids and/or solids that are contained therein. For example an apparatus is described in WO 91/15768 in which sample vessels are arranged eccentrically on a motor axis and are rotated by the motor alternately in a clockwise and anti-clockwise direction. Another device is described in U.S. Pat. No. 5,580,524 in which rotatably mounted vessels are rotated by contacting the external surface of the vessels with a rotating disk. This document describes that reversing the direction of rotation can suspend magnetic particles in a liquid.
The apparatuses described in the documents WO 91/15768 and U.S. Pat. No. 5,580,524 have the disadvantage that the washing and mixing cannot be adapted to the specific circumstances of the respective vessel content. No information is given in these documents about the possibility of adapting the rotation process in order to optimize the results. In contrast the present invention has the advantage that by changing the mixing process it is possible to achieve a considerable improvement in the mixing efficiency. In particular the present invention allows the use of mixing sequences in which two or more different mixing processes are combined. It has been experimentally demonstrated that the use of such mixing sequences greatly increases the mixing efficiency. A further advantage of apparatuses and methods according to the invention is that they effectively prevent splashing and aerosol formation. Furthermore the invention enables the meniscus deflection to be kept small such that mixing is also possible in almost completely filled vessels without a closure.